In the healthy human, there are billions of bacteria colonizing the intestine. This intestinal microflora is a complex community of microorganisms that plays a role in several intestinal diseases such as inflammatory bowel disease, irritable bowel syndrome (IBS), and colon cancer. Among these, IBS is a common disorder in children, affecting up to 25% of school-age children and adolescents. However, our knowledge of the changes in microflora in IBS and other diseases is incomplete. There is a lack of quantitative measurements of microflora differences between healthy and ill individuals. Moreover, while both children and adults suffer from these disorders, the majority of previous studies were carried out in adults. Our lack of understanding of microflora dynamics during intestinal diseases retards the development and evaluation of new and exciting medicines, such as probiotics. Our long-term goal is to study microflora dynamics during intestinal disorders and to assess the use of probiotics as treatment options for such illnesses. In this project, using a custom microarray specifically designed by us to study microflora structure in the human gastrointestinal tract, we will quantitatively compare the microflora composition in the feces of healthy children with that in children with IBS;and we will test if the use of probiotic VSL#3 to treat children suffering from IBS will lead to specific changes in microflora composition to mirror that of healthy children. The potential for screening of microflora in patients suffering from intestinal disorders before the onset of probiotic treatment can provide useful information on microflora status that would help in the choice of an appropriate probiotic therapy. At the same time, the ability to assess changes in microflora during probiotic treatment will provide direct information on the effect of probiotics on the microflora community. PUBLIC HEALTH RELEVANCE: Intestinal microflora is a complex community of microorganisms that is believed to play a role in several intestinal diseases such as irritable bowel syndrome (IBS). Though there is evidence that the gut flora of IBS patients differs from that of the healthy individuals, we still lack the understanding of specific microflora changes in IBS. The paucity of such knowledge leads to difficulties in interpretation of the results of IBS treatments, particularly those involving probiotics. The research proposed in this application will profile microflora composition in healthy children and in children with IBS undergoing probiotic treatment. The comparisons of microflora composition between these children will i) provide information on microflora status during IBS in children and its changes as a result of probiotic treatment, ii) expedite the evaluation and development of new therapeutic options such as probiotic agents aimed to restore normal microflora composition;and iii) establish the base of knowledge on microflora composition necessary for further studies of probiotic effects on microflora.